MTB cassette on road bike

lphtc

Is this possible?

I am looking for a cheap alternative to get lower gears for climbing. Basically, my road bike has a standard 39-52T chainset and a 13-26T eight-speed cassette (shimano)

I was wondering whether or not I could replace my current cassette for a 11-30T cassette (MTB shimano 8-speed)?

both, my current cassette and the MTB one are HG chains compatible.

Would it work fine? I am not sure but I think rear derailleur could be the the big limiting factor as most road derailleurs are only able to support a cassette up to 26-27T.

How do I know whether my RD can support 30T or not?

cheers

nicklouse

sure but an MTB rear mech will also be needed to be fitted.

lphtc

I've just found the Technical Service Instructions for shimano rear derailleur RD-2300.

Well, I am a bit confused.

According to the document specifications it says:

Total capacity 35 teeth or less
Largest sprocket 26 T
Smallest sprocket 12 T
Front chainwheel tooth difference 22T

Does it mean I could use my rear derailleur with any 8 speed HG cassette up to 35T?

stigofthedump

There are two things to consider.
1 There needs to be enough movement using the B limit screw for the top jockey wheel to miss the sprokets. This screw moves the mech away from the cassette to give you enough clearance. Generally it has a lot of adjustment available.
2 The mech needs to take up the slack when you are using small ring small sproket and allow for big ring large sproket. You should avoid 'crossing' the chian, ie big big or small small so if you are careful with gear selection you can run a short cage mech with a large gear range. I have done this on a MTB (when i was a weight weenie)

I ran an 8 speed MTB cassette on a road bike in the alps successfully without changing the mech ( shimano ex300) a few years ago with no problem. You might need to try it to see.

maddog 2

lphtc wrote:

Does it mean I could use my rear derailleur with any 8 speed HG cassette up to 35T?

No.

It means you can get 26t officially and probably 27 or 28 is possible in practice. 30t would be pushing it though I suspect, even with the tension screw on max.

You could give it a try. Dropout/hanger length plays a part too, so it could work, maybe.

Butterd2

nicklouse wrote:

sure but an MTB rear mech will also be needed to be fitted.

+1

Twostage

I've got a 28 on my tiagra when the tech docs say 27 is the max.

BrianTrousers

Why don't you just swap your front chainrings if you want lower gearing?

lphtc

Hi all, thanks!

BrianTrousers wrote:

Why don't you just swap your front chainrings if you want lower gearing?

That is another option...

I read that is not possible to change the smaller chainring due to the distance of the bolts.

Is it possible to change both front rings (from 52/39 to 50/34) and keep the crankarm? Or I would I have to replace the whole chainset?

night_porter

Changing the rear mech to an MTB one isn't very complicated and you are then guaranteed it will work.

By using an Acera rear mech you will be able to put up to a 34 tooth cassette on and the mech will cost less than 20 quid, brand new. You can even replace the mech without breaking the chain.

You might need to learn how to set the limit screws and re-index but there is plenty of help on the web (Park tools website) and they are skills worth having.

This is a lot simpler and cheaper than changing the chainrings and you will make your life a lot easier!

satanas

Try it with the mech you have before spending any money. Shimano are conservative when rating derailleurs and there's an excellent chance what you have will worrk fine. I've used 30T rear cogs with road derailleurs plenty of times, and even 32T will sometimes work, if only just.

jejv

The real answer is a compact triple. There's enough range in what cogs will go on a compact triple to satisfy most people. Might be worth working out what that would cost.

If you go for a larger cassette, you will very likely need a longer chain, or bad things will happen to your rear mech.

Going from 26 to 30 is not going to help much. One extra gear.
By all means try it with your existing rear mech - it might work, but bear in mind that without a longer chain, attempting to engage large & large may wreck your rear mech.

About the best you can do without some drastic changes to the transmission is a 32 on the back. Yes you can get a 34, but with a huge jump to the 34.

If your existing 13-26 isn't too worn, you can make a 13-32 from your 13-26 and a (shimano) 11-32, taking the 15,21,23,26 out of the 13-26, and adding the 21,24,28,32 from the MTB cassette, so you have 13-15-17-19-21-24-28-32. That avoids the 20% midrange jump in the MTB cassette.

There's a long sticky thread in the Road Beginners section on how to get lower gears.

Eyon

I know this isnt exactly the solution you are after, but I also use a 2300 groupo and am after a double chainset and a narrow cassette as the riding in my area doesn't need super low gears.

If you are interested in a 600 mile old chainset/mech/L.shifter for a strait swap let me know. All in good condition apart from the obvious heel rub. Chainset is 52/42/30 and will get you up pretty much every hill in existence with the 26T cassette.

39-26 gearing gives a ratio of 1.5
30-25 gives 1.15, a lot lower!

Drop me a PM if you're interested